Marah Hardt: What Can We Learn From The Sex Lives Of Fish? Marine biologist Marah Hardt is fascinated with the mating habits of marine life. If we want to save the oceans, she says we have to understand the weird and whimsical sex that helps populate it.

What can we learn from the sex lives of fish?

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It's the TED Radio Hour from NPR. I'm Manoush Zomorodi. And today's show is a Love Letter to the Ocean.


ZOMORODI: You know, I have had this song stuck in my head since I watched your talk. Would it be OK if I played it for you?

MARAH HARDT: Yeah, I'm game.


COLE PORTER: (Singing) Romantic sponges, they say, do it.

ZOMORODI: Do you recognize it?


PORTER: (Singing) Oysters down in Oyster Bay do it.

HARDT: I do. This is the great Cole Porter's "Let's Fall In Love."

ZOMORODI: "Let's Do It, Let's Fall In Love."

HARDT: "Let's Do It." That's right. "Let's Do It, Let's Fall In Love." Yeah, he's actually a little dirtier than I'm giving him credit for (laughter).


PORTER: (Singing) Even lazy jellyfish do it.

ZOMORODI: This is Marah Hardt. She's a marine biologist and an author.

HARDT: The name of my book is "Sex In The Sea: Our Intimate Connection With Sex-Changing Fish, Romantic Lobsters, Kinky Squid And Other Salty Erotica Of The Deep."


PORTER: (Singing) Why ask if shad do it?

ZOMORODI: I mean, the song just goes on and on about electric eels doing it, lazy jellyfish doing it, goldfish in the privacy of their bowls doing it.

HARDT: Yeah.

ZOMORODI: What's your reaction to that song as a person who specializes in the sex lives of fish?

HARDT: Oh, well, I rock out to that song. It's fantastic.

ZOMORODI: (Laughter).

HARDT: But it completely misses so much of the more colorful and honestly kinky components because the fun part isn't that they do it. The fascinating and fun and important part is how they do it.


HARDT: For example, clownfish.


ALBERT BROOKS: (As Marlin) Nemo.

ALEXANDER GOULD: (As Nemo) First day of school.

BROOKS: (As Marlin) Nemo, don't move. Don't move. You'll never get out of there.

HARDT: Everybody knows "Finding Nemo." They know clownfish. But what they don't realize is that clownfish species all start life - any individual that's born starts life as a male. And then later in life, he transitions into a female.


HARDT: Yeah, yeah. And they pair up - a male and a female will pair up. And for them to make the most babies, what they want is for the bigger of the two to be female. And this is because unlike in mammals where - for example, with humans - right? - a woman is born with all the eggs she will ever have, in fish, the bigger the female is, the more eggs she can carry. And since sperm is really cheap to make, a small male energetically can make a lot of sperm. He can make enough sperm to fertilize all of a large female's eggs.


HARDT: And what's happening is the female is actually sort of doing this psychological warfare, and she kind of bullies her mate, the male. And she kind of keeps him from sort of getting too aggressive where he would actually then begin to transition into a female. He then bullies all these smaller males to say don't you guys get any wrong ideas about competing with me for access to this female's eggs. So his bullying kind of keeps the juveniles in this almost, like, suspended premature state.

And then when that female dies, the male can very quickly transition into a female. And then the next largest juvenile matures into a male. And then they will become the mating couple. And nobody has to leave the anemone and go find a date or a mate, which is much safer.

ZOMORODI: That is crazy.

HARDT: It's crazy (laughter).


ZOMORODI: Who knew that clownfish could be so intriguing?

HARDT: You just can't make this stuff up. You know, nature has the best imagination of all.

ZOMORODI: But the fact that you and I and most people know very little about how clownfish mate and very rarely think about how marine life reproduce, Marah says that's a problem.

HARDT: Because these animals reproduce in a different way, our actions affect the success of sex in the sea in ways that we might not anticipate right when it's most important.

ZOMORODI: So for clownfish - they're often caught and sold as aquarium pets.

HARDT: And the bigger fish - right? - are the ones that tend to be the more attractive for sale. So if you imagine on a reef, you go around and you start pulling off all the big clownfish, you're taking all the females.

ZOMORODI: And taking all the females completely disrupts the life cycle of an entire school of clownfish.

HARDT: You skew the sex ratio. You're making it harder for those individuals that are left behind to actually find their mates, or you're forcing them to transition in a - under conditions sooner than they would. And that's it's going to actually decrease the amount of offspring that is being produced.

ZOMORODI: Which causes a ripple effect for every creature connected to the clownfish. So just imagine how we are messing with the mating habits of all kinds of marine life, the ones we know about and the ones we don't.

HARDT: It's so varied, the way that animals have sex in the sea. And it's so different that we really need to take that step back and start to shift the way that we act and shift some of our behaviors so that we can respect the way that life reproduces there rather than thwarting them.


ZOMORODI: All to say, we need to know how marine life do it. And so now let's dive deeper and move from the coral reefs of the South Pacific down to the cold, cold romantic waters off the coast of Maine.


HARDT: Take Maine lobster. They don't look that romantic or that kinky. They are both.

ZOMORODI: Here's Marah Hardt on the TED stage.


HARDT: During mating season, female lobsters want to mate with the biggest, baddest males. But these guys are really aggressive, and they'll attack any lobster that approaches, male or female. Meanwhile, the best time for her to mate with a male is right after she's molted, when she's lost her hard shell. So she has to approach this aggressive guy in her most vulnerable state. What's a girl to do?


HARDT: Her answer - spray him in the face repeatedly with her urine.


HARDT: Mmm hmm. Under the sea, pee is a very powerful love potion.


HARDT: Conveniently, lobsters' bladders sit just above their brains, and they have two nozzles under their eyestalk with which they can shoot their urine forward. So the female approaches the male's den. And as he charges out, she lets loose a stream of urine and then gets the hell out of there.


HARDT: Only a few days of this daily dosing is all it takes for her scent to have a transformative effect. The male turns from an aggressive to a gentle lover. By the week's end, he invites her into his den.

ZOMORODI: OK. So urine as an aphrodisiac, also kind of a chill pill - so he invites her in for a nightcap. Is that kind of it? They go for it?

HARDT: So she will occupy the den with him, and they'll hang out for a while - a couple of days. They'll hunt. They'll feed. They'll sleep, do their...


HARDT: ...Lobster stuff. And then when she feels that her molt is imminent, she will circle around front of him. And then they go through this wonderful ritual. He sort of bows his head down and puts his big claws out in the sand, and she sort of rises herself up. And she takes one of her big claws, and she'll tap him on one shoulder and then the other.


HARDT: And we call this - yeah. We call this knighting 'cause it really looks like that. And we...

ZOMORODI: You are chosen.

HARDT: You are chosen. And we're pretty sure it means, not only are - you are chosen, but don't go anywhere 'cause all of this is about to happen.


HARDT: She then goes to the back of the den. And for the next few hours, she will molt. So she sort of slips out of her shell if you will. That whole time, the male guards over her. He'll walk back and forth from the front of the den to her. He'll sort of stroke her with his antenna and his walking legs, his small legs. And lobsters - their taste buds are on their feet, on their - those little legs. So he's actually kind of like tasting her, licking her. That's where, like, the kinky part comes in. So he's sort of guarding over her, tasting her, caring for her. And then she sort of gives him a signal that she's ready.

And now, at this point, she literally is like a blob. She can't support her own weight. She cannot stand up. She can't really move. And so he scoops her up using his walking legs and forms almost like a hammock and holds her and rolls her over so that they're belly to belly - basically in the missionary position - and sort of cradles her there. And then he inserts these two special little fins that he has sort of at the base of his tail that slot into that pouch, and he delivers his sperm packet. And then he very gently lays her back down, and that's it. That's the sex. But then for the next few days, he will guard the front of that den while her new shell is hardening.


HARDT: And then when she's ready, she stands up, says thank you very much, leaves the den. They probably never see each other again. And then the next female will arrive at his doorstep and start spraying him in the face with her pee, and the whole thing repeats.

ZOMORODI: It's like marine erotica kind of. Like, it's...

HARDT: So, right. You go down a lot of rabbit holes when you're...


HARDT: ...Writing a book about sex in the sea. And I would never want anyone to look at the history of my computer. I'd be terrified at what they'd find.


ZOMORODI: So in terms of the role that humans are playing in lobster sex - I mean, in terms of I guess I should say disrupting lobster sex, like, can you explain that?

HARDT: Sure. So the ability for her love potion, for her urine to work as a love potion depends on her urine having certain chemical signals - right? - and the male having receptors that can receive those signals. And one of the things that we're doing in the ocean through climate change is we're making the oceans more acidic. We're actually changing the fundamental chemistry of seawater. That might scramble the message as it's passing through the seawater. And we know that more acidic seawater is known to damage certain kinds of receptor cells. It's affecting smell and chemical signaling in many species.

So imagine if her love potion didn't work, right? That disrupts the whole strategy that lobster reproduction is based on. And it's not just climate change where this happens, right? If there's a big pollution event - you know, oil spill or runoff from land - that can change the chemical signature of water and mask or mess up the ability of animals to detect those scents.


HARDT: Dive deeper, and sex gets even stranger.


HARDT: Fanfin anglerfish live at about 3,000 feet below the surface in the pitch black waters. And the males are born without the ability to feed themselves. To survive, he has to find a female fast. Meanwhile, the female, who is 10 times bigger than the male - 10 times - she lets out a very strong pheromone with which to attract mates to her. So this tiny male is swimming through the black waters, smelling his way to a female. And when he finds her, he gives her a love bite. And this is when things get really weird.

The bite itself triggers a whole bunch of chemical reactions. And the first is that, basically, his jawbone starts to dissolve. His tissue kind of starts to almost, like, melt and fuses with her body. Their circulatory systems entwine. And almost all of his internal organs start to dissolve...


HARDT: ...Except for his testes. His testes, actually, like, kick up into, like, full-blown maturity mode. And he starts producing sperm.


HARDT: In the end, he's basically a permanently attached, on-demand sperm factory for the female.


HARDT: It's a very efficient system.


HARDT: But this is not the kind of mating strategy that we see on a farm, right? I mean, this is weird. It's really strange. But if we don't know that these kind of strategies exist or how they work, we can't know what kind of impacts we may be having, even in the deep sea.


ZOMORODI: Presumably, with the anglerfish, this must have been one of the hardest discoveries to make. And if you don't know that these wild procreation activities are going on, then you can't know when you're impacting them, right? As humans, we don't know what we don't know.

HARDT: It's - yeah, absolutely. We don't know what we don't know. So there's - I think there's two lessons there, so first is precautionary approach all the time. Assume you might be doing harm. And make sure that when you're putting a new behavior or new activity into place that you're proving no harm. In many places on land, if you're going to put up a development or you're going to allow industry to come in and do some sort of extractive activity, they have to do an environmental impact assessment. They have to show they're not going to hurt endangered species or disrupt the ecosystem. We don't tend to do that in the ocean. And some of that is because we think the oceans are endless and abundant forever.


HARDT: And now we know that's - right? - that's not the case. So taking a precautionary approach is really important - and correcting some behaviors that we know we've gotten wrong, so things like fishing on spawning aggregation. So again, for fish who release their sperm and eggs into the water, many of them form these annual, amazing, huge sex parties, right? They're like giant orgies.


HARDT: And you'll have tens of thousands if not hundreds of thousands of fish that will all gather in one place at one time. Often, it's, like, a full moon party. They do - they love the full moon. There's reasons for that - but big, full moon sex party. And while they're reproducing, let them reproduce. That's not a good time to come in and fish.


HARDT: It's easy, right? For the fishers, it's easy because they can catch a lot of the biggest fish all at once. But you're tapping into the principal rather than taking the interest, right? You're actually cutting off the ability of that population to make more fish for you for the next year.

ZOMORODI: Do you, like, use these examples and sort of the same sort of sexy language about fish, like, when you're talking to people who are overfishing or people who might be polluting the oceans? Like, are - do you say, like, let's talk about fish sex?

HARDT: (Laughter).

ZOMORODI: Is that your hook?

HARDT: Some - (laughter) I tend to use the fish hook more with folks who I'm trying to get to just care, just genuinely start to awaken to the fact that they are connected to the ocean. I honestly - I can't tell you how many times in bars I've just, like, struck up a conversation with a stranger over this.

ZOMORODI: (Laughter).

HARDT: Right? Like, it's just - it's great bar trivia. And you can...

ZOMORODI: You talk dirty to them.

HARDT: You talk dirty. You can slide in a little fun factoid, and then you're off and running. And the thing that's so marvelous is that, honestly, people are curious about nature. They are curious about oceans. And whether they admit it or not, they are curious about sex. Everybody is.

ZOMORODI: (Laughter).


HARDT: And so it's a wonderful bridge to start to engage in those conversations without being heavy-handed, without it all being doom and gloom either - right? - 'cause just talking about collapse of our ocean ecosystems and the threat of climate change, that doesn't inspire. It doesn't bring solutions to the table.


HARDT: Right? Instead it's like, wow, isn't this crazy? And what can we do to make sure that lobsters keep getting to have their kinky sex lives?


ZOMORODI: Marah Hardt is a marine biologist and the author of the book "Sex In The Sea." She's also a conservationist at the nonprofit Future of Fish. You can see her full talk at

I think it's time to update Cole Porter's lyrics.

HARDT: (Laughter) I know. I was just thinking about that. I was like, you know, clownfish in there anemones do it. But they all start males and then transition to females, and there's this crazy psychological warfare where they control one another's maturation, and they're stuck in prepubescent limbo. You know, it doesn't really work. But...



ZOMORODI: On the show today, a Love Letter to the Ocean. I'm Manoush Zomorodi, and you're listening to the TED Radio Hour from NPR.

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